exploring the advantages of wet fermentation in a

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London Conference on Biodegradable Waste Jürgen Martens script updated 28-09-2004

Examining Alternative Waste Treatment Technologies for Biodegradable Waste

15th October 2004 – Olympia Conference Centre, London

Exploring the Advantages of Wet Fermentation

in a Mechanical-Biological Waste Treatment Plant (MBT)

Dipl.-Phys. Jürgen Martens

The new national and European legislation demands that in future all waste must be

treated prior to landfilling. One interesting option are waste-to-energy schemes with

the aim to use as much of the waste as possible to produce secondary fuel.

Mechanical-biological waste treatment – usually referred to as “MBT” - and

corresponding process technology are more and more moving to the centre of

attention. They will be a major issue for the coming years.

MBT is very complex, a combination of different stages of treatment and equipment:

First, we have the mechanical treatment, the sorting of the waste. The next step is

treatment of the biological fraction, usually by rotting or fermentation. MBT is

completed by facilities for process air treatment, energy generation, and water

treatment.

My presentation today does not deal with the mechanical part of mechanical-

biological waste treatment, the simple reason being that in general all systems work

with the same kind of treatment here. It is, however, important to know that the

material sorted from the waste is the high-caloric fraction. This material can later be

used as secondary fuel.

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Which kind of treatment?

The question we should ask is: Which kind of treatment is most appropriate to treat

the biological fraction? Traditional aerobic composting (rotting) or anaerobic

digestion, as an alternative?

(see slides no 8, 9, 10)

Rotting

“Rotting” (composting) is often considered the most suitable method of treatment, not

only in Germany, but also in the UK. Spain and Portugal are an exception.

Rotting is indeed a practical method to treat small amounts of waste – especially

where green and relatively dry biowaste is concerned. But with rotting, emissions and

energy generation remain of secondary importance.

The challenge we face with the new EU Landfill Directive is to treat an enormous

quantity of waste independent of its composition. In this case, economical and

environmentally friendly treatment is only feasible with anaerobic processes such as

fermentation.

Fermentation

Fermentation of the biological fraction of the waste has considerable advantages:

(see slides no 11, 15, 19)

Lower cost of investment, in comparison to rotting.

The facility requires less space.

Conversion of carbon to carbon dioxide does not consume energy, but

actually generates energy!

The facility generates more energy than it requires for its operation.

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The system is closed. All suspensions are pumped through the system, the

digestors are gastight.

Emissions are reduced, because the fermentation process requires less

process air.

Less manpower is required.

The process is continuous and suitable for automation.

Compared to other methods of treatment fermentation is the most economical

and ecologically sound solution.

MBT components provided by HAASE Energietechnik AG

(slide no 28)

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For anaerobic treatment a number of technical variations are possible:

A) Dry fermentation

This method did not meet with much success, for the following reasons:

The biological conversion ratio remains quite low.

High costs are incurred for process technology and technical equipment,

because the matter can not be pumped.

B) Wet fermentation + afterrotting

(see slides no 11, 12, 13, 14)

This solution is currently implemented in Germany and in Spain.

Features:

Provides residual waste in accordance with legal requirements.

Offers the same advantages as a “wet fermentation” process. (see above)

Aerobic aftertreatment such as tunnel rotting or other automatical-

mechanical systems still have the disadvantages experienced

with “rotting”.

C) Wet fermentation + wet oxidation

(see slides no 15, 16, 17, 18)

Features:

This combination has all the advantages of (B). The difference to

(B) is that the afterrotting process is indeed a liquid process.

We call this “wet oxidation”.

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Simple process technology, all matter can be pumped through the facility.

Produces less emissions than method (B).

Requires less manpower than method (B).

This is the most economical and ecological solution to create residues

suitable for landfilling.

D) Wet fermentation + thermal drying

(see slides no 19, 20, 21, 24)

Features:

This process combination has all the advantages of method (B), but here

we do not have an aerobic treatment at the end. The final product is not

suitable for landfilling, but it is a very good secondary fuel and has the

calorific value of brown coal.

This is the most economical and ecologically sound solution to convert the

biological fraction of the waste into secondary fuel.

On a long-term basis (C) and (D) will prove to be the most interesting solutions to

pre-treat the waste, because almost the entire energy potential of the waste is

exploited. And with regard to emissions they obviously have the lowest impact on the

environment.

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The “idex-system” : Concept for innovative landfilling of MBT residues

(slide no 39)

The “idex-system”

Finally, I would like to present the “idex-system” as a possible solution to dispose of

residues from waste treatment.

Here, we say goodbye to the kind of landfill operation we experienced for the last 30

years.

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The alternative offered by the “idex-system” is to use high-pressure and turn the

residues into dimensionally stable cubes. These cubes will then be stacked away

with high-lift trucks. This modern “landfill” rather has the features of an industrial high-

rise warehouse …

The benefits of this innovative system are so very obvious that I am convinced it will

probably not even take 10 years to make us forget about “old” landfill technology.

Juergen Martens

Represented in the UK by

Clarke Energy Limited

Power House, Senator Point Phone: +44 (151) 546 4446

South Boundary Road Fax: +44 (151) 546 4447

Knowsley Industrial Park eMail: [email protected]

Liverpool L33 7RR (UK) Internet: www.clarke-energy.co.uk

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